Fuel injection pump for internal combustion engines

Abstract

A fuel injection pump in which a relief channel is formed which communicates with the pump working chamber and is arranged to be blocked by a valve means, associated with a valve actuating means responsive to a pressure varying with engine r.p.m., during starting of the engine so that the fuel injection quantity is increased. Thus, improved starting characteristics of the engine can be obtained. Said relief channel may comprise a first channel communicating with the pump working chamber, and a second relief channel which has a portion thereof extending in the pump plunger to terminate in an outer periphery of the bottom end of said plunger and is so disposed as to communicate with the pump suction chamber after a predetermined delivery stroke length or prestroke has been executed. Communication between said first and second relief channels is adapted to be interrupted by said valve means at less than a predetermined engine r.p.m. As another advantagenous arrangement, the relief channel may comprise a first relief channel which consists of a port having one end communicating with the pump working chamber and the other end terminating in an outer periphery of the plunger and a communication channel having one end terminating in an inner periphery of the plunger barrel and the other end arranged for communication with a lower pressure zone, and a second relief channel allowing a restricted flow rate and communicating with the pump working chamber. The port and communication channel of said first relief channel are so disposed as to communicate with each other at the beginning of the delivery stroke of the plunger. Said first and second relief channels are arranged to be simultaneously blocked by said valve means during starting of the engine.

What is claimed is: 
     
       1. A fuel injection pump for an internal combustion engine, which comprises: a housing; a suction chamber defined within said housing; a barrel mounted within said housing; a plunger mounted within said barrel for axial and rotary motion therein; a pump working chamber defined by the housing, the barrel and a top end of the plunger and arranged for communication with said suction chamber; outlet pressure lines for connecting said pump working chamber with associated injection nozzles; a fuel quantity setting member slidably fitted on a bottom end of said plunger; a first relief channel having one end thereof communicating with said pump working chamber; a second relief channel having a portion thereof extending in the plunger to have one end thereof terminating in an outer periphery of the bottom end of the plunger, said end of said second relief channel being so disposed as to disengage from an end edge of said fuel quantity setting member to communicate with said suction chamber after the plunger has executed a predetermined delivery stroke length; a valve means provided across said first and second relief channels for controlling communication therebetween; and a valve actuating means communicating with a pressure source supplying a pressure varying with engine r.p.m.; wherein said valve means is arranged to be actuated by said valve actuating means responsive to said varying pressure to interrupt communication between said first and second relief channels at less than a predetermined engine r.p.m. 
     
     
       2. A fuel injection pump as recited in claim 1, in which said first relief channel comprises: an axial blind bore formed within a top end portion of said plunger with one end thereof terminating in a top end surface of said plunger; an annular groove formed in an outer periphery of the plunger; a transverse bore having one end thereof communicating with said blind bore and the other end terminating in said annular groove; and a communication channel having one end thereof terminating in an inner periphery of said barrel and the other end communicating with said valve means; and said second relief channel comprises: a blind bore formed within a bottom end portion of said plunger with one end thereof radially terminating in an outer periphery of the plunger; an annular groove formed in an outer periphery of the plunger; a transverse bore having one end thereof communicating with said blind bore and the other end terminating in said last-mentioned annular groove; and a communication channel having one end thereof terminating in an inner periphery of the barrel and the other end connected to said valve means. 
     
     
       3. A fuel injection pump as recited in claim 1, in which said valve means comprises: a bore formed within said housing in communication on one side with said first and second relief channels and on the other side with a zone under a lower pressure; a piston slidably mounted within said bore; and a spring arranged for urging said piston in an axial direction of the bore against the force of said valve actuating means; wherein said first and second relief channels are so disposed that communication therebetween is interrupted by displacement of said piston. 
     
     
       4. A fuel injection pump as recited in claim 3, in which said piston has an interior thereof formed with a channel extending in H-shaped path which includes two ports so located as to simultaneously register with respective associated ends of said first and second relief channels. 
     
     
       5. A fuel injection pump as recited in claim 3, in which said valve actuating means comprises a passage means having one end thereof communicating with one end of said bore and the other end with said pressure source supplying a pressure varying with engine r.p.m. 
     
     
       6. A fuel injection pump as recited in claim 5, in which said passage means comprises a supply line formed within said housing with one end communicating with said suction chamber which is supplied with a fuel supply pressure by a fuel pump arranged for rotation at a speed proportional to engine r.p.m. and the other end disposed for communication with said pump working chamber, and an annular groove formed in an outer periphery of said barrel with one side thereof intersecting with said supply line and the other side communicating with said bore.